New insights into electrospray ionization of patulin

Patulin is a mycotoxin produced by several fungal species, mainly by Penicillium spp. and Aspergillus spp. Since patulin-producing fungi are widely spread, this toxin has been detected in food (fruit- and vegetable-based products, cereal products, cheese), feed and even in mouldy water-damaged dwellings. Co-occurrence of patulin with other mycotoxins has also been reported [1]. Patulin is commonly analyzed by liquid chromatography with UV detection. Liquid chromatography coupled to mass spectrometry (LC-MS/MS) is considered as a more specific tool for mycotoxin detection and confirmation. However, the implementation of this technique for the determination of patulin, especially in the context of multi-mycotoxin analysis, is limited due to ionization problems. In this study, the effect of different solvents, mobile phase additives and pH on the ionization and fragmentation pattern of patulin was investigated. The preliminary results showed that under alkaline conditions and using methanol as organic modifier, an intense and stable signal for the methanol-adduct of patulin was obtained in the positive electrospray ionization mode. The fragmentation of this protonated methanol-adduct gave a strong and stable product ion signal. The production spectra were overall more useful than those obtained with the protonated or the deprotonated molecule. These findings indicate the possibility of using the protonated methanol-adduct of patulin for its identification and quantification by LC-MS/MS. Further results that will be presented include the optimization, by means of experimental design, of the parameters that have an influence on the formation of the protonated methanol-adduct of patulin and on its fragmentation behaviour, as well as the inclusion of this toxin in a multi-mycotoxin LC-MS/MS method. This study is the first report of the LC-MS/MS determination of patulin using its protonated methanol-adduct. References: [1] Nielsen KF (2003) Mycotoxin production by indoor molds. Fungal Genetics and Biology. 39: 103-117

Delivery and reveal of localization of upconversion luminescent microparticles and quantum dots in the skin in vivo by fractional laser microablation, multimodal imaging, and optical clearing

Delivery and spatial localization of upconversion luminescent microparticles [Y 2 O 3 ;Yb, Er] (mean size ~1.6 μm) and quantum dots (QDs) (CuInS 2 ZnS nanoparticles coated with polyethylene glycol-based amphiphilic polymer, mean size ~20 nm) inside rat skin was studied in vivo using a multimodal optical imaging approach. The particles were embedded into the skin dermis to the depth from 300 to 500 μm through microchannels performed by fractional laser microablation. Low-frequency ultrasound was applied to enhance penetration of the particles into the skin. Visualization of the particles was revealed using a combination of luminescent spectroscopy, optical coherence tomography, confocal microscopy, and histochemical analysis. Optical clearing was used to enhance the image contrast of the luminescent signal from the particles. It was demonstrated that the penetration depth of particles depends on their size, resulting in a different detection time interval (days) of the luminescent signal from microparticles and QDs inside the rat skin in vivo. We show that luminescent signal from the upconversion microparticles and QDs was detected after the particle delivery into the rat skin in vivo during eighth and fourth days, respectively. We hypothesize that the upconversion microparticles have created a long-time depot localized in the laser-created channels, as the QDs spread over the surrounding tissues

Amplification of SERS Signal of Methotrexate Using Beta-Cyclodextrin Modified Silver Nanoparticles

The paper describes the use of native β-cyclodextrin (CD) for the modification of silver nanoparticles (AgNPs) in order to improve the determination of the anticancer drug methotrexate (MTX) using surface-enhanced Raman spectroscopy (SERS). A control experiment with unmodified AgNPs showed that the strong SERS signal of MTX can only be achieved in alkaline media. However, competitive interactions and the strong background signal of human body fluid components significantly challenge MTX determination in real samples. While previous reports propose the use of thorough sample pretreatment (e.g., solid phase extraction), the application of CD-modified AgNPs increases the SERS signal of MTX in neutral media by seven times which enables simplifying the analysis and improving its accuracy by reducing the influence of endogenous components of body fluids. A detailed study of the synthesis conditions (CD concentration and reaction time) and SERS registration conditions (pH, NaCl concentration, dilution of urine samples) was performed to maximize the analytical signal and signal-to-noise ratio. The final assay was tested for MTX determination in artificially spiked samples of real human urine. The results demonstrated that MTX can be determined within the concentration range suitable for therapeutic drug monitoring (20–300 μg mL−1) with satisfactory precision (6–15% RSD), accuracy (95–111% apparent recovery), and limit of detection (0.3 μg mL−1)

A Facile Approach to the Hydrothermal Synthesis of Silica Nanoparticle/Carbon Nanostructure Luminescent Composites

Luminescent carbon nanostructures (CNSs) have been intensively researched, but there is still no consensus on a fundamental understanding of their structure and properties that limits their potential applications. In this study, we developed a facile approach to the synthesis of luminescent composite SiO2 nanoparticles/CNSs by the targeted formation of a molecular fluorophore, as the significant luminescent component of CNSs, on the surface of a silica matrix during a one-stage hydrothermal synthesis. Silica nanoparticles were synthesized by reverse microemulsion and used as a matrix for luminescent composites. The as-prepared silica nanoparticles had a functional surface, a spherical shape, and a narrow size distribution of about 29 nm. One-stage hydrothermal treatment of citric acid and modified silica nanoparticles made it possible to directly form the luminescent composite. The optical properties of composites could be easily controlled by changing the hydrothermal reaction time and temperature. Thus, we successfully synthesized luminescent composites with an emission maximum of 450 nm, a quantum yield (QY) of 65 ± 4%, and an average size of ~26 nm. The synthesis of fluorophore doped composite, in contrast to CNSs, makes it possible to control the shape, size, and surface functionality of particles and allows for avoiding difficult and time-consuming fractionation steps

Silanized luminescent quantum dots for the simultaneous multicolor lateral flow immunoassay of two mycotoxins

A critical point for the successful development of a fluorescent quantum dot (QD)-based immunoassay is maintaining the high fluorescence quantum yield of QDs during hydrophilization and bioconjugation. In this paper, we carefully designed CdSe/CdS and CdSe/CdS/ZnS core-shell heterostructures and extended them with silica coating of different surface composition allowing preservation of fluorescence quantum yield as high as 70% in aqueous media. The silanized QDs containing epoxy and carboxy surface groups were bioconjugated with monoclonal antibodies. The synthesized fluorescent conjugates were used in a multicolor lateral flow immunoassay for simultaneous determination of two mycotoxins. Zearalenone and deoxynivalenol were chosen as a proof of concept. Cutoff levels for the zearalenone and deoxynivalenol detection were adjusted to be at 40 and 400 mu g kg(-)(1), respectively, complying with the European Commission regulation. Validation of the developed test was performed by analysis of 34 naturally contaminated maize and wheat samples; as a confirmatory method, LC-MS/MS was used

A systematic assessment of the variability of matrix effects in LC-MS/MS analysis of ergot alkaloids in cereals and evaluation of method robustness

The study presents for the first time a systematic investigation of matrix effects in the LC-MS/MS analysis of ergot alkaloids in cereals. In order to assure the accuracy of the results, several approaches to minimize/eliminate matrix effects were investigated including variation of ionization techniques, chromatography and sample preparation on different grain types and grain varieties. It was revealed that the use of UPLC and careful choice of sample preparation might reduce signal suppression/enhancement. In general, ergometrine was found to be the most susceptible among the ergot alkaloids studied, but none of the used approaches suggested a total elimination of matrix effects; only less than half of its MS signal could be recovered. The late-eluting compounds were less affected by matrix components in all conditions tested. Further, the robustness of the applied LCMS method was checked by means of a fractional factorial design. The results indicate that small changes to the sample preparation parameters, namely pH and concentration of extraction buffer, shaking time, drying temperature and extraction volumes, did not significantly (α=0.05) affect the recoveries of ergot alkaloids